1. Field
The disclosed embodiments concern a technique for fabricating an aircraft fuselage whose outer skin is executed in composite material. The technique of the disclosed embodiments allow the outer skin to be executed, in composite material, around the internal structure of the fuselage, thus facilitating the assembly of said internal structure. The disclosed embodiments also concern an aircraft fuselage obtained by such a fabrication technique.
The disclosed embodiments find application in the field of aeronautics, and in particular in the field of fabricating aircraft fuselages.
2. Brief Description of Related Developments
The fuselage of an aircraft is the body of the aircraft. The wing surface, the vertical stabilizers, the landing gear, the engines, and numerous other elements are fastened to the fuselage. The fabrication of the fuselage thus constitutes an important step in the construction of an aircraft.
Traditionally, the fuselage of the aircraft is a hollow body executed in metal. This hollow body is composed of metal panels mounted and fastened around an internal structure, generally metal, called the internal framework of the aircraft. The metal panels are assembled with fasteners and form, once assembled, the outer skin of the aircraft. Such metal fuselages are very widespread nowadays. However, they present the disadvantage of being heavy, since the fuselage is entirely metal. Moreover, they present the disadvantage of inserting joints, between the metal panels, which constitute excess thickness. This excess thickness increases the weight and can cause drag when the aircraft is in flight, which is disruptive from the aerodynamic viewpoint.
In order to reduce the weight of the fuselage, aeronautical engineers are trying to replace some metal elements with elements made of composite materials. These composite materials are used in particular to execute one or several parts of the fuselage of the aircraft, for example for the ventral fairing of the aircraft. These parts of the fuselage are generally panels executed starting with dry fibers pre-coated with resin. These panels are fabricated by preparing sheets and/or fabric pieces made of dry fibers pre-coated with a thermoset resin, placing these sheets and/or fabric pieces in a mold and then heating the whole. Under the effect of heat, the resin polymerizes, permitting the fiber reinforcement to preserve the shape of the mold. After cooling, the mold is removed. Such a fabrication technique permits the fabrication principally of panels, that is, pieces with an open profile, since the mold has to be removed after shaping and cooling. It allows the fabrication of a hollow body with difficulty, in particular with a changing shape, for example, hollow bodies with a conical shape.
In order to allow the fabrication, in composite material, of a portion of the fuselage with a changing shape, a technique exists which consists of fabricating a section of the outer skin of the fuselage of an aircraft. This section of outer skin is achieved by wrapping sheets of fibers pre-coated with resin around a mold having the desired shape. The mold may be a hollow cylinder. The mold thus wrapped with pre-coated fiber sheets is heated on order to polymerize the resin. After cooling, the laminate obtained shapes the outer skin of the aircraft. This outer skin is detached from the mold, either by sliding or by disassembly in place and then removal from the mold. When the outer skin has been executed, the internal framework is inserted inside the outer skin, piece by piece, or in a group of basic parts positioned on complex frame structures. The internal framework of an aircraft is an assemblage of frames and other structural parts, such as beams and decking. The internal framework is thus installed by inserting each frame and structural part of the framework inside the outer skin, then by fastening each of these pieces from the inside of said outer skin. When the pieces of the internal framework are too large, they are divided up into several portions and inserted, portion by portion, into the outer skin and then fastened to each other with rivets.
Such a technique is difficult to implement due in particular to the large surface area of the outer skin to be detached from the mold. The outer skin may in addition include elements of the type presenting excess thickness which still increase the difficulties of unmolding. Moreover, this technique takes a relatively long time to implement, since it necessitates the insertion and the fastening, as basic groups, or piece by piece, or even portion by portion, of all the parts forming the internal framework, inside the outer skin.